It is a common requirement to hold a component (or “workpiece”) in position on a fixture associated with an automated machine tool (for example a Computer Numerically Controlled Milling Machine) while it is machined. For annular components, such as casings, it is known to hold the component within guides on a fixture on a location diameter, with a minimal clearance between the guides and the circumference of the casing to lead the component to the correct position on the fixture. The casing is then clamped to the fixture. If necessary, shims may be used to centre the component in the correct position on the fixture. The disadvantage of such equipment and method is that any play or misalignment between the component and fixture may result in machining tools removing material from incorrect locations or drilling holes to incorrect depths. Play and misalignment may also result in incorrect measurements when measured using an automated measuring device (for example a Coordinate Measuring Machine), perhaps leading to the component being incorrectly rejected. If an annular component is clamped incorrectly, it may become distorted (for example eccentric), resulting in features being machined to incorrect shapes.
Hence a means for supporting a workpiece during a machining operation which locates the workpiece in a correct location without distortion is highly desirable.